An artist's conception shows a SBIRS satellite monitoring an area of Earth's surface.

How Satellites Give Clues About Malaysia Jet Attack in Ukraine

A family of satellites known as the U.S. Space Based Infrared System, or SBIRS, was probably key to determining that a surface-to-air missile took down the Malaysia Airlines Boeing 777 jet over Ukraine on Thursday. The satellites fly in geosynchronous orbit, 22,300 miles above the planet, and use infrared sensors to detect heat sources on the ground, such as rocket or missile plumes. Five are operational at all times, and they're supplemented by infrared sensors on other satellites that are part of the Defense Support Program, or DSP.

Since the 1970s, the principal mission of the DSP family has been to detect launches of intercontinental ballistic missiles and sea-launched ballistic missiles via their plumes. During the Vietnam War, defense officials found that the satellites could also detect the signatures of smaller missile launches, midair explosions and nuclear tests. SBIRS readings are downloaded and initially analyzed at Buckley Air National Guard Base in Aurora, Colorado. Last month, Lockheed Martin won a $1.9 billion contract to expand the satellite system.